The issue occurs when IP phone A calls IP phone B on line 1, phone B goes offhook and phone B presses the Hold softkey. The handset of phone B is put back on the cradle. The call on hold does not resume if phone B proceeds in any of these instances:
The user picks up the handset, presses the line on which the call is on hold and presses the Resume softkey. Pressing the Resume softkey multiple times may resume the call, but 90 percent of the calls still fail.
The user presses the Speaker key and receives a dial tone and presses the line on which the call was on hold. The user then presses the Resume softkey once or multiple times. However, the call is not resumed.
Pressing the Resume key stops the Music On Hold (MOH) from being streamed to phone A, but the call never gets connected.
These symptoms are observed for calls between any two IP phones or a Public Switched Telephone Network (PSTN) and an IP phone.
This issue is described in Cisco bug ID CSCec21007: Intermentally phone will not send OpenReceiveChannelAck. It is observed only on IP phones with a shared line.
The Cisco CallManager traces reveal that once you press the Resume softkey on phone B, CallManager sends aOpenReceiveChannel message to phone A. However, phone A never sends a OpenReceiveChannelACK message back. Therefore, the call on hold does not resume.
To resolve this issue, perform these steps:
To retrieve a call on hold, press the Line key on which the call is on hold, bypassing the handset and speakerphone.
This bug has been fixed in Cisco CallManager 3.3(3)SR02. Upgrading Cisco CallManager to version 3.3(3)SR02 should fix the problem.
For more information, refer to Cisco bug IDs CSCec21007 and CSCeb19725: One way and no way audio between IP Phones.